The present invention relates to the field of production fluid vessels for separating sand and other solid materials from water and other hydrocarbon fluids produced from a well. More particularly, the present invention relates to an improved system for removing solid materials from a separator vessel while the vessel is in-service.
Bulk separator vessels remove sand and other solid materials from fluids produced from hydrocarbon wells. Sand is often produced from unconsolidated production zones within an oil and gas well. Because sand is highly abrasive and also tends to pack-off flow constrictions, sand removal extends equipment life and reduces maintenance requirements.
One type of bulk separator operates on the principles that sand is more dense than the hydrocarbon fluids, that oil and other hydrocarbon liquids are less dense than water produced with the hydrocarbons, and that these materials tend to separate over time. The well fluids are deposited into a large separator vessel and the sand settles to the vessel bottom. Water also collects in the vessel bottom and rises to a selected mid point level having an exit weir which screens sand movement while permitting excess water to be diverted to an exit nozzle. An "oil bucket" has an intake at a higher elevation than the water exit weir, and collects oil and other hydrocarbons floating near the top of the water. An oil bucket exit nozzle discharges oil and other hydrocarbons from the vessel interior.
The separator vessel permits relatively crude separation of sand, water and oil on a continuous basis. While the water and oil are continuously discharged from the vessel interior, sand accumulates in the vessel bottom until the system is closed down for cleaning. After system operations are discontinued, the vessel is opened and sand is typically discharged from the vessel interior by hydrojetting operations. Previously, the equipment was manually operated by maintenance personnel. This contact with potentially toxic hydrocarbon fluid residue in the vessel interiors requires ventilation, atmospheric monitoring of the vessel site, and personnel safety training and management.
Conventional vessel cleaning also closed down hydrocarbon production during the turnaround time necessary to clean the separator vessel. Lost production is highly expensive and reduces operating productivity. Various techniques have been developed to provide in-service separator vessel cleaning services. One technique pushes a lance and nozzle into the vessel interior. The lance is manually pushed through a packer seal to prevent uncontrolled leakage of fluids from the vessel interior. In an improved system, a hydraulic ram pushes the lance nozzle into the vessel interior. The lance is pushed through the packer seal until the nozzle extends into the vessel interior. Compressed air or a pressurized fluid is then pumped through the lance body and nozzle tip so that the force generated by the nozzle discharge dislodges solid materials within the vessel interior. The dislodged solid materials are withdrawn through an exit port or valve.
Although this technique provides for solids removal without disrupting separation operations, this process is inefficient for several reasons. Because the lance body must be sufficiently flexible to pass through conduit and into the vessel interior, force exerted on the lance body within the vessel interior by the nozzle discharge causes the lance body to whip around in the vessel interior. This uncontrolled movement can damage the lance body, nozzle tip, and interior vessel components, and can leave uncleaned areas within the vessel as the lance moves indiscriminately within the vessel.
This technique creates another significant problem in conventional cleaning operations. The nozzle indiscriminately stirs up solid materials within the vessel interior and re-mixes the solid materials with the water and hydrocarbon fluids. By reversing the settling processes provided by the separator vessel, sand and other solid materials are suspended in the water and hydrocarbon fluids and can re-enter the oil bucket and water collection areas within the vessel. After the sand has entered such areas, the sand will travel downstream with the hydrocarbons and water streams or will pack-off within the oil bucket and water collection areas.
Accordingly, a need exists for an improved separation system that provides inservice cleaning of separator vessels. The system should not disrupt separation operations, should efficiently remove sand and other solid materials from the vessel, and should limit maintenance personnel exposure to hazardous materials.